package org.yaosheng.algorithm.SegmentTree;

/**
 * Created by yaosheng on 2022/7/24.
 * 线段树
 */
public class SegmentTree<E> {

    private E[] data;
    private E[] tree;
    private Merger<E> merger;

    public SegmentTree(E[] arr,Merger<E> merger){

        this.merger = merger;

        data = (E[])new Object[arr.length];
        for(int i = 0;i < arr.length;i ++)
            data[i] = arr[i];

        tree = (E[])new Object [4 * arr.length];
        buildSegmentTree(0,0, data.length - 1);
    }

    // 在treeIndex的位置创建表示区间[l...r]的线段树
    private void buildSegmentTree(int treeIndex,int l,int r){

        if(l == r){
            tree[treeIndex] = data[l];
            return;
        }

        int leftTreeIndex = leftChild(treeIndex);
        int rightTreeIndex = rightChild(treeIndex);

        int mid = l + (r - l) / 2;
        buildSegmentTree(leftTreeIndex, l, mid);
        buildSegmentTree(rightTreeIndex, mid + 1, r);

        tree[treeIndex] = merger.merge(tree[leftTreeIndex], tree[rightTreeIndex]);
    }

    public int getSize(){
        return data.length;
    }

    public E get(int index){

        if(index < 0 || index >= data.length)
            throw new IllegalArgumentException ("Index is illegal.");

        return data[index];
    }

    // 返回完全二叉树的数组表示中，一个索引所表示的元素的左孩子节点的索引
    private int leftChild(int index){
        return 2 * index + 1;
    }

    // 返回完全二叉树的数组表示中，一个索引所表示的元素的右孩子节点的索引
    private int rightChild(int index){
        return 2 * index + 2;
    }

    // 返回区间[queryL,queryR]的值
    public E query(int queryL,int queryR){

        if(queryL < 0 || queryR >= data.length || queryR < 0 ||
                queryR >= data.length || queryL > queryR)
            throw new IllegalArgumentException ("Index is illegal.");

        return query (0,0,data.length - 1,queryL,queryR);
    }

    // 在以treeID为根的线段树中[l...r]的范围里，搜索区间[queryL...queryR]的值
    private E query(int treeIndex,int l,int r,int queryL,int queryR){

        if(l == queryL && r == queryR)
            return tree[treeIndex];

        int mid = l + (r - l) / 2;
        int leftTreeIndex = leftChild (treeIndex);
        int rightTreeIndex = rightChild (treeIndex);

        if(queryL >= mid + 1)
            return query (rightTreeIndex,mid + 1,r,queryL,queryR);
        else if(queryR <= mid)
            return query (leftTreeIndex,l,mid,queryL,queryR);

        E leftResult = query (leftTreeIndex,l,mid,queryL,mid);
        E rightResult = query (rightTreeIndex,mid + 1,r,mid + 1,queryR);

        return merger.merge (leftResult,rightResult);
    }

    // 将index位置的值更新为e
    public void set(int index,E e){

        if(index < 0 || index >= data.length)
            throw new IllegalArgumentException ("Index is illegal.");

        data[index] = e;
        set (0,0,data.length - 1,index,e);
    }

    // 在以treeIndex为根的线段树中更新index的值为e
    private void set(int treeIndex,int l,int r,int index,E e){

        if(l == r){
            tree[treeIndex] = e;
            return;
        }

        int mid = l + (r - l) / 2;
        int leftTreeIndex = leftChild (treeIndex);
        int rightTreeIndex = rightChild (treeIndex);

        if(index >= mid + 1)
            set (rightTreeIndex,mid + 1,r,index,e);
        else
            set (leftTreeIndex,l,mid,index,e);

        tree[treeIndex] = merger.merge (tree[leftTreeIndex],tree[rightTreeIndex]);
    }

    @Override
    public String toString(){

        StringBuilder res = new StringBuilder ();
        res.append ("[");

        for(int i = 0;i < tree.length;i ++){
            if(tree[i] != null)
                res.append (tree[i]);
            else
                res.append ("null");

            if(i != tree.length - 1)
                res.append (", ");
        }
        res.append ("]");
        return res.toString ();
    }
}
